"Nowhere in there did anyone invent anything to make email addresses more accessible to people."
That's not what it says ... it says trying to make technology more accessible to people. user@hostname email addresses, as opposed to the old UUCP bang paths, does indeed make technology more available to people. (FWIW, I worked on the ARPANET at UCLA and was there when the IMP arrived in 1969, so I do know a little something about this topic.)
Uh nope. Nothing like that happened. SNDMSG allowed sending messages between users on the same computer. Then Ray Tomlinson added his file transfer code to SNDMSG and needed a symbol to separate user names from the host names, and he picked the @ Nowhere in there did anyone invent anything to make email addresses more accessible to people.
The only reason there were host names and not just numbers on the right hand side was because ARPAnet really has grown and just a few months before Tomlinson's invention names were added https://tools.ietf.org/html/rfc226 (20 hosts! really, big network) but this, again, predates email addresses.
Another very early example of email in 1970 was integrated into the NLS (short for Online System) at the SRI ARC https://www.dougengelbart.org/pubs/papers/scanned-original/1... but this used usernames and not addresses "mail distribution was addressed by peoples Idents with no need to know or specify which host they used".